16-1: Genes and VariationGregory Shook
Darwin’s HandicapsMendel’s work was published but ignoredDidn’t know how traits are inheritedDidn’t know how variation appeared
Modern Evolutionary Theory1930’s, molecular biology/genetics combined
with Darwin’s theoriesDNA structure allowed the molecular nature
of mutations to be illustrated
How Common is Genetic Variation?Many genes have 2 allelesSome genes ‘invisible’ because it involves
biochemical processesFish, reptiles, and mammals are typically 4-
8% of their genes heterozygous
Variation and Gene PoolsA gene pool is all the genes, including
different alleles, that are present in a population
Relative frequency of an allele is the number of times that allele is in the gene pool
In genetic terms, evolution is any change in the relative frequency of alleles in a population
Sources of Genetic VariationMutations: A mistake in the genetic sequence
Some may be neutral, some may change a phenotype Change may have an effect on fitness, may not
Gene shuffling ***Sexual Reproduction***Individuals don’t look identically like either
parent In meiosis, each part of a homologous pair of
chromosomes migrate independently Humans have 8.4 MILLION different gene
combinations Crossing over further increases changes to the
genotype
Single-Gene and Polygenic TraitsThe number of phenotypes possible depends
on how many genes control that traitA single-gene trait is controlled by one gene,
and has two alleles Widow’s peak in humans is an example
Polygenic TraitsTraits controlled by many genes are called
polygenic traitsEach gene often has different allelesHuman height is an example